The identity function with a restricted type, for conveniently
declaring that some value should have type Turn. For example,
rotation . asTurn . fromRational constructs a rotation from a
rational value considered as a Turn. Without asTurn, the angle
type would be ambiguous.

The identity function with a restricted type, for conveniently
declaring that some value should have type Rad. For example,
rotation . asRad . fromRational constructs a rotation from a
rational value considered as a value in radians. Without asRad,
the angle type would be ambiguous.

The identity function with a restricted type, for conveniently
declaring that some value should have type Deg. For example,
rotation . asDeg . fromIntegral constructs a rotation from an
integral value considered as a value in degrees. Without asDeg,
the angle type would be ambiguous.